(CNN) -- A local official said substantial efforts to mitigate risks proved no match for Mother Nature in Washington state, where a devastating landslide left 16 people dead -- a figure the state's governor said Wednesday is all but guaranteed to rise.
Rescue crews used bulldozers, shovels and their hands to comb through the muddy morass in Snohomish County, looking for any signs of life or death. Some 175 people remain unaccounted for in the landslide, which buried 49 structures in up to 40 feet of mud in a square mile area located about an hour north of Seattle.
Could this disaster -- or at least, the human toll -- have been prevented?
After a smaller landslide struck the same area in 2006, officials invested millions of dollars to reduce the risk, and residents felt safe, Snohomish County Emergency Management Director John Pennington told reporters Wednesday.
"We really did a great job of mitigating," he said.
Pennington cited a 2010 Natural Hazard Mitigation Plan, which contains a chapter pointing to the area that was swept away as one of several "hot spots." Residents knew the area was "landslide-prone," he added -- but that doesn't mean they anticipated an event on the scale of what happened Saturday.
"Sometimes, big events just happen," Pennington said.
Governor predicts a sharp rise in death toll
Pennington called this year's heavy rains, which have saturated the county of more than 700,000 residents, "amazing." He also raised the possibility that a small earthquake noted in the area at the time of the slide could have played a role.
"I don't have those answers now," he said.
Asked if the county could have better prepared for the landslide, he said, "I'm not sure that we could have." He added, "It haunts me ... we did everything we could have done."
Washington Gov. Jay Inslee noted that landslides hit the state on a regular basis, but said, at this stage, "we don't know" if there were missed warning signals.
What the governor does believe is the death toll will rise greatly. So much time has passed since the last survivors were rescued, and search teams have been sobered by the "discouraging" reality that they have not found more people protected by a car or a structure, Inslee said.
"I don't think anyone could reach any other conclusion," Inslee said in an interview with CNN's "The Lead with Jake Tapper."
Area long known to be unstable, says geologist
The area had long been known to be unstable, said Daniel Miller, a geomorphologist in Seattle who co-wrote a report in 1999 for the Army Corps of Engineers that looked at options to reduce sediments from landslides in the area.
The 56-page report identified "a very large volume of material that could potentially become unstable," he told CNN Wednesday in a telephone interview.
"That's the portion that appears to have failed in this event," he said. But he cautioned that his study never assessed risk.
Landslides had occurred in 1951, 1967, 1988 and 2006, he said; though none resulted in deaths, at least one of them -- the 2006 event -- damaged houses. "I would not have had a house in that location," he said.
His report study may have simply been shelved, he said.
Miller said the fault lies, in part, with the county and, in part, with the people who decided to live in a place with a history of landslides.
Though a state ordinance asks counties to map landslide hazard zones, it has not been translated into zoning restrictions, he said.
And, though no one may have told landowners in the landslide zone about the risk, that wouldn't absolve them of responsibility, he said. "As landowners, we have some responsibility to be aware of our surroundings and their risks," he said.
It comes down to how much risk a person, or a community, is comfortable with, he said. "Ultimately, there was no way to know when a landslide would occur," he said.
"We had indications that it could be very large. But we didn't know it would be very large. We didn't know when it would occur ... but we did know it could occur."
He personally would not have stomached the risk accepted by residents, he said. After a landslide in 2006, he saw new buildings being raised in the neighborhood. "My reaction was to shake my head and say, 'This is nuts.'"
Finding the missing
In his news conference, Emergency Management Director Pennington said he had met Wednesday with state representatives and was to meet later later in the day with FEMA representatives to begin the process of integrating federal and state resources to get the area back on its feet. "We have a federal declaration for direct federal assistance," he said. "It can be very complicated."
Two National Guard helicopters were aiding in the effort, which remained a rescue effort, he said.
Finding the missing will be tough. In Oso, population about 180, and Darrington, population 1,350, houses are buried under mud that has the consistency of quicksand.
President Barack Obama, in the Netherlands on Tuesday, asked that "all Americans to send their thoughts and prayers to Washington state and the community of Oso."
Obama said he had spoken with Gov. Inslee and signed an emergency declaration.
-- CNN's John Crawley, Jason Hanna and Amy Chillag contributed to this report.
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